Method of inserting, rotating and releasing a spring-loaded artificial disk

ABSTRACT

A rotating, locking, spring-loaded disk implant for stabilizing adjacent vertebrae. The implant is substantially rectangular in cross-sectional shape with minimal height and maximal width. The implant is inserted into the space between two adjacent vertebrae from which a portion of the intervertebral disk has been removed and, when positioned in the disk space, rotated to bring the sides of the rectangularly-shaped implant defining the width of the implant, with its larger dimension, into engagement with the bodies of the adjacent vertebrae. A portion of the implant is biased away from the implant and into contact with the adjacent vertebrae to provide a cushioning effect between the implant and the vertebra. A lock is then secured to the implant to resist further rotation of the implant in the disk space.

BACKGROUND OF THE INVENTION

The present invention relates to a spring-loaded intervertebral diskimplant for stabilizing two adjacent vertebrae. More specifically, thepresent invention relates to rectangularly-shaped disk implants whichare expanded in the middle portion and are used as an alternative tospinal fusion.

Treatment of a herniated disk in the neck and in the lumbar regioncontinues to be a challenging field of medicine. The classical treatmentfor a ruptured disk is diskectomy, i.e., removal of the disk frombetween the vertebrae. In this process, all or a portion of theintervertebral disk is removed, leaving a defect that may bother thepatient throughout the rest of their life and compromising the normalinteraction between disk and adjacent vertebrae. A procedure that issometimes used as an alternative is to replace the disk space with abone graft, usually bone chips cut from the patient's iliac crest,bringing about fusion of the vertebrae above and below the disk,eliminating the empty space between the vertebrae.

Diskectomy with fusion is not ideal because the replaced bone does nothave the function of the cartilaginous tissue of the disk, i.e. nocushioning effect, and has complications because of several factors.First, conventional bone plugs used to pack the disk space do notconform to the space of the disk because the disk bulges maximally inthe center. The disk space is wider in the middle and narrower at itsanterior and posterior ends. For this reason, many commerciallyavailable bone plugs have four contact points, i.e. two at each of thefront and back of the disk space. Secondly, access to the disk is fromthe side of the dorsal spine of the adjacent vertebrae, leaving a spacethat is “off-center” relative to the bodies of the adjacent vertebraesuch that the stability of the implant is even more problematical thanmight be apparent from the limited contact resulting from the shape ofthe intervertebral space. Another complication is the possibility ofinfection or other conditions that may require removal of the implant.Also, if the bone pieces do not fuse, they may eventually extrude out ofthe disk space, pressuring the nerve roots. The most significantdisadvantage is that fusion eliminates all motion at the joint betweenthe two vertebrae, as well as the shock-absorbing/cushioning function ofthe disk.

Various prosthetic disk plugs, or implants, are disclosed in the art,but all are characterized by limitations of not conforming to the shapeof the disk space, lack of stability when inserted off-center, inabilityto be removed, or other disadvantages. For instance, U.S. Pat. No.4,863,476 (and its European counterpart, EP-A-0260044) describes anelongated body divided longitudinally into two portions having a camdevice movable therebetween for increasing the space between the twobody portions once inserted into the disk space. However, that device isgenerally cylindrical in shape such that the only contact points betweenthe device and the vertebral bodies are at the front and back of thedisk space, creating increased likelihood of instability and generallyrendering that device unsuitable for use after partial diskectomy.

The art also discloses intervertebral disk prostheses such as U.S. Pat.Nos. 3,867,728, 4,309,777, 4,863,477, 4,932,969, Applicant's own U.S.Pat. No. 5,123,926, and French Patent Application No. 8816184 that mayhave more general contact with the adjacent disks, and spinal jointprostheses as described in U.S. Pat. No. 4,759,769, but which are notintended for use in fusion of the disks. However, the utility of suchdevices is also limited by a number of disadvantages, in particular, thesame lack of cushioning described above in connection with prior artdisk plugs and implants. Further, those implants and prostheses thatattempt to address this cushioning problem have generally failed becausethey are not capable of supporting the load imposed upon them by theactive post-surgical patient. Further, many prior implants andprostheses require removal of the disk. Removing the disk is not totallyundesirable because removing the intervertebral disk does help preventproblems from recurrent disk herniation through the opening into theintervertebral disk space. However, as with all surgical procedures, itis desirable to utilize as much existing structure as possible and tominimize invasiveness. One reason it is desirable to retain as much ofthe original disk as possible is that if an implant subsequently fails,or if further surgical intervention is indicated for reasons such asinfection, the only alternative that is generally available afterremoval of the intervertebral disk is fusion.

There is, therefore, a need for a device capable of stabilizing thevertebrae adjacent an intervertebral disk that overcomes the variousdisadvantages and limitations of spinal fusion procedures and the diskplugs and implants that are used in such procedures, and it is an objectof the present invention to provide apparatus and methods for meetingthat need.

There is also a need for a device that overcomes the disadvantages andlimitations of prior intervertebral disk prostheses and so it is also anobject of the present invention to provide apparatus and methods formeeting that need.

There is also a need for a device that can be implanted into the diskspace in a procedure that decreases the likelihood of recurrent diskherniation and it is also an object of the present invention to provideapparatus and methods for meeting that need.

There is also a need for a device that combines the function of the diskby retaining as much of the undamaged disk as possible, and byfunctioning in a similar manner to provide the cushioning effect of thedisk, and it is an object of the present invention to provide apparatusand methods for meeting that need.

There is also a need for a device that not only functions to provide thecushioning effect of the intervertebral disk but that also provides theopportunity for the repair of the remaining portion of the disk, and itis an object of the present invention to provide apparatus and methodsfor meeting that need.

Another need that is apparent from the limitations and disadvantages ofprior procedures, disk plugs, and prostheses is the need for a devicethat maintains the function of the intervertebral disk when implantedbetween adjacent vertebrae and that is capable of being implanted in asurgical procedure that is minimally invasive and that does not requireremoval of the entire intervertebral disk, and it is therefore also anobject of the present invention to provide apparatus and methods formeeting that need.

Another need that is apparent from the limitations and disadvantages ofprior procedures, disk plugs, and prostheses is the need for a devicethat works with the structure of the intervertebral disk space tomaintain as much of the normal function of the disk as possible, and itis also an object of the present invention to provide apparatus andmethods that combine the properties of cushioning that can be obtainedby utilizing the remaining portion of the disk, stability by utilizing ametal implant, shock absorption by biasing a portion of an insert intoengagement with the adjacent vertebrae, a hydrogel that functions tofill gaps in the disk space and to help reconstruct and/or preventrecurrent herniation of the remaining portion of the disk, and ifnecessary, a medical grade adhesive that helps to hold the remainingportion of the disk together and/or bond the hydrogel to the diskmaterial and/or seal off the opening into the disk space, therebymeeting that need.

Another need that is apparent is the need for a device that is capableof supporting the load imposed upon it when implanted in the disk spacewhile also providing the cushioning function of the naturalintervertebral disk and it is also an object of the present invention toprovide apparatus and methods for meeting that need.

SUMMARY OF THE INVENTION

These needs are met in the present invention by providing a vertebraldisk stabilizer comprising an elongate implant with a lock having asurface formed thereon for bearing against either or both of theadjacent vertebrae detachably mounted to one end of the implant toprevent rotation of the lock relative to the implant. When mounted tothe implant to resist rotation of the implant, the bearing surface ofthe lock is oriented at an angle of approximately 90° to the height ofthe implant. The implant is provided with an insert that is biased intocontact with one or both of the adjacent vertebrae to provide acushioning effect between vertebrae.

In another aspect, the present invention provides a method of cushioningbetween an implant in the intervertebral disk space and the vertebraeadjacent the disk space comprising the steps of inserting an elongateimplant into the intervertebral disk space with the sides of the implantcontacting the adjacent vertebrae, biasing an insert portion of theimplant away from the implant and into contact with the adjacentvertebrae, and restraining the implant against further rotation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded, perspective view of a first embodiment of avertebral disk stabilizer constructed in accordance with the teachingsof the present invention.

FIG. 2 is an exploded, perspective view of a second embodiment of avertebral disk stabilizer constructed in accordance with the teachingsof the present invention.

FIG. 3 is an exploded, perspective view of a third embodiment of avertebral disk stabilizer constructed in accordance with the teachingsof the present invention.

FIG. 4 is an exploded, perspective view of a fourth embodiment of avertebral disk stabilizer constructed in accordance with the teachingsof the present invention.

FIG. 5 is an exploded, perspective view of a fifth embodiment of avertebral disk stabilizer constructed in accordance with the teachingsof the present invention.

FIG. 6 is an exploded, perspective view of a sixth embodiment of avertebral disk stabilizer constructed in accordance with the teachingsof the present invention.

FIG. 7 is a perspective view of the stabilizer of FIG. 6 showing a bandfor minimizing the height to facilitate insertion into theintervertebral disk space.

FIG. 8 is an exploded, perspective view of seventh embodiment of avertebral disk stabilizer constructed in accordance with the teachingsof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the figures, a first embodiment of a disk stabilizerconstructed in accordance with the teachings of the present invention isindicated generally at reference numeral 20 in FIG. 1. Stabilizer 20 isintended to be implanted between the bodies of two adjacent vertebrae inthe disk space from which a portion of the intervertebral disk has beenremoved, i.e. by simple diskectomy and small laminotomy.

The vertebral disk stabilizer 20 is comprised of an elongate implant 22,lock 24, and means for detachably mounting the lock 24 to one end 25 ofthe implant 22. In the presently preferred embodiment shown, themounting means takes the form of a bolt 26 passing through a bore 28 inlock 24, the threads of bolt 26 engaging complementary threads in thewalls of the bore 30 in the end 25 of implant 22. A lock nut (not shown)may optionally be provided for resisting the loosening of the bolt 26once lock 24 is mounted to implant 22 in the manner described below.

In more detail, implant 22 is comprised of first and second sides 32 andthird and fourth sides 34 providing a substantially rectangularly shapedcross-section. The height of the rectangularly shaped cross-section isdefined by first and second sides 32 and the width is defined by thethird and fourth sides 34 and, as is apparent by comparison of theheight and width, the width of implant 22 is less than the height. Aswill be explained below, height is minimized to facilitate insertion ofthe second end 36 into, and positioning of implant 22 in, the disk spacefrom which a portion of the intervertebral disk has been removed andwidth is maximized so that, when implant 22 is rotated by approximately90°, implant 22 provides the desired distraction of the adjacentvertebrae. Third and fourth sides 34 are arched from one end of implant22 to the other to provide the portion of implant 22 intermediate theends 25 and 36 with a height that is larger than the height at the ends25 and 36. Because the sides 32 of implant 22 are substantially flat andthe sides 34 are arched from one end 25 to the other end 36, implant 22is described as being a bi-planar, bi-convex implant. The bi-convexsides 34 of implant 22 are optionally provided with a plurality of teeth(not shown) for biting into the adjacent vertebrae to help resistanterior-posterior movement of implant 22 in the disk space as explainedin more detail below. The end 36 of implant 22 is provided with a flare,or “whale tail,” 38 for this same reason, it being critical to resistsuch anterior-posterior movement so as to reduce the likelihood ofinjury to the nerves of the spinal cord both during insertion of implant22 into the disk space and after implantation.

In the embodiment shown, lock 24 is substantially square when viewedfrom the end 40 along the axis of the bore 28 therethrough and“U”-shaped when viewed from the side. The inside surfaces 42 of the arms44 of the “U”-shaped lock 24 are flat for contacting the first andsecond sides 32 of implant 22 to prevent rotation of lock 24 relative toimplant 22 when lock 24 is mounted to implant 22 and secured thereto bybolt 26. The sides 32 of implant 22 are provided with a key 46 that isreceived in a complementary-shaped keyway 48 formed in the surface 42 ofthe arms 44 of lock 24 to facilitate assembly of lock 24 to implant 22;those skilled in the art who have the benefit of this disclosure willrecognize that (as shown in FIGS. 6 and 7) the key 46 may be located onthe lock 24 and keyway 48 may be located on implant 22 without anydifference in the manner in which those component parts function.Although not shown in FIGS. 1-6, in the same manner as described belowin connection with FIGS. 6 and 7, those skilled in the art willrecognize that the mouth of the keyway 48 at the ends of the arms 44 oflock 24 may be wider than the width of the key 46 to facilatateinsertion of keys 46 into keyways 48.

The sides of the square end 40 of lock 24 provide surfaces 50 forbearing against the bodies of the adjacent vertebrae as also explainedin more detail below. It will be recognized by those skilled in the artwho have the benefit of this disclosure that the bearing surfaces 50need not be flat and that the end 40 of lock 24 need not be square.Other shapes and configurations may be utilized as needed to insure thatmovement of lock 24, and the implant 22 once lock 24 is mounted toimplant 22, is limited by engagement of the bodies of the adjacentvertebrae by the vertebral bearing surfaces 50. The purpose of thebi-planar, middle expanded, bi-convex implant 22 is to enable insertionof the implant 22 into the disk space and turning by approximately 90°to increase the disk height and stabilize the disk space. The purpose oflock 24 is to lock implant 22 against instability when in the verticalposition so as to maintain the disk height thereafter.

An applicator (not shown) of the type described in U.S. Pat. No.5,658,336, which patent is hereby incorporated into this specificationin its entirety by this specific reference thereto, is mounted to theend 25 of implant 22 by screwing the threaded end of the applicator intothe threaded bore 30 in implant 22. When the applicator is screwed allthe way into bore 30, so as to prevent relative movement therebetween,implant 22 is inserted into the disk space with the wide sides 32 (sothat the height of implant 22 is of minimal dimension) proximate thebodies of the adjacent vertebrae and rotated in the disk space byapproximately 90° using the applicator so that the minimally-dimensionedsides 34 are proximate the bodies of the adjacent vertebrae so as tomaximize the height of implant 22 in the disk space. The procedure forplacement of the implant 22 is set out in more detail below. Theapplicator is then detached from implant 22 by rotating in the oppositedirection while rotation of implant 22 is restrained.

After implant 22 has been rotated so as to maximize height in theintervertebral disk space and the applicator is detached from theimplant, and before lock 24 is mounted to implant 22 to prevent rotationof implant 22 in the disk space, bolt 52, which extends into the portionof the threaded bore 54A in implant 22 in the end 25 of implant 22 andthe portion 54B in the insert portion 56 of implant 22, is backed out ofimplant 22. Backing bolt 52 out of threaded bore 54B releases insert 56,which is biased away from the landing 58 in the implant 22 by springs60, from a first, compressed position to a second position in which theinsert 56 floats on springs 60 so that the portion 34A of the side 34 ofimplant 22 comprising insert 56 contacts the body of a vertebraeadjacent the disk space. As set out in more detail below, biasing insert56 toward the adjacent vertebrae (away from the landing 58 of implant22) in this fashion provides the cushioning function that is lackingfrom prior known intervertebral implants. The pistons 62 on theunderside 57 (the side adjacent landing 58) of insert 56 are received incomplimentary-shaped and sized recesses, or blind bores, 64 to maintainalignment of the insert 56 with implant 22 as insert 56 moves relativeto implant 22, and a stop 66 formed on one end of insert 56 is engagedby the lip 68 formed by the cap 70 that is secured to implant 22 by capscrew 71 to limit movement of insert 56 away from landing 58. Of coursethe springs 60 bear against the landing 58 of implant 22 and theunderside 57 of insert 56 to bias insert 56 away from landing 58. Theadjacent surfaces 72A, 72B and 74A, 74B of insert 56 and implant 22,respectively, are shaped in complementary curves so as to assist inmaintaining alignment between insert 56 and implant 22 as insert 56moves relative to implant 22. Those skilled in the art who have thebenefit of this disclosure will recognize that the adjacent surfaces72A, 72B and 74A, 74B may be provided with a key and keyway or otherstructure that functions to maintain alignment between insert 54 andimplant 22 as insert 54 moves relative to implant 22 in the disk spaceand that the present invention contemplates any and all such structurethat functions in this manner to accomplish the result of maintainingalignment.

Referring now to FIG. 2, a second embodiment of a stabilizer constructedin accordance with the teachings of the present invention is indicatedgenerally at reference numeral 76. Stabilizer 76 includes most of thesame component parts as shown in the stabilizer 20 shown in FIG. 1 andthe reference numerals utilized in FIG. 2 are therefore the same as areutilized in describing the component parts of stabilizer 20 shown inFIG. 1 (and for the same reason, the same numbering scheme is alsoutilized in describing the embodiments shown in FIGS. 3-7). Rather thanbeing provided with a pair of coil springs such as are shown in FIG. 1,the stabilizer 76 shown in FIG. 2 is provided with leaf spring 78 thatis received within the cavity 80 formed on the underside 57 of insert56. In spite of this structural difference in the means for biasinginsert 56 away from the landing 58 of implant 22, stabilizer 76functions in the same manner as stablilizer 20.

A third embodiment of a stabilizer constructed in accordance with theteachings of the present invention is indicated generally at referencenumeral 82 in FIG. 3. Stabilizer 82 differs from stabilizer 20 (FIG. 1)in that the threaded portion of bolt 52 is provided with a weak point,indicated at reference numeral 84, and that either a portion of bore 54Aextending through implant 22 or a portion of the bolt 52 proximate thehead thereof is unthreaded. Bolt 52 initially resides in the bore 54extending through the end 25 of implant 22 and into insert 56 to holdinsert 56 in the first position in which the coil springs 60 arecompressed and the underside 57 of insert 56 is proximate the landing 58of implant 22 while implant 22 is inserted into the disk space and thenrotated approximately 90° as described briefly above and in more detailbelow. Bolt 52 is then backed out of bore 54 until it extends only partway into the bore 54B in insert 56, freeing insert 56 from the first,compressed position in which the underside 57 of insert 56 is proximatethe landing 58 of implant 22 so that it is biased away from landing 58by springs 60. The bolt 52 is then broken at the point 84 and the headand broken portion of bolt 52 are removed from the bore 54A and fromimplant 22. Of course removing the bolt 52 from the end 25 of implant 22allows a close fit between lock 24 and the end 25 of implant 22 whenlock 24 is mounted thereto. The portion of bolt 52 that remains in thethreaded portion of bore 54A, after bolt 52 was backed part way out ofbore 54, extends only part way into the bore 54B in insert 56 so thatinsert 56 is retained in alignment with implant 22 by movement of theremaining threaded portion of bolt 52 in the channel 86 formed in thesurface 72A of insert 56, the bottoming out of bolt 52 in channel 86also acting as a stop to limit the movement of insert 56 away fromlanding 58. Referring to FIG. 4, a fourth embodiment of a stabilizerconstructed in accordance with the teachings of the present invention,shown at reference numeral 88, is likewise provided with a bolt 52having the same break point 84 as shown in the stabilizer 82 (FIG. 3),unthreaded proximal portion of bore 54A, and channel 86, all of whichfunction in the same manner as described in connection with theembodiment shown in FIG. 3

A fifth embodiment of a stabilizer constructed in accordance with theteachings of the present invention is designated generally by referencenumeral 90 in FIG. 5. Stabilizer 90 is likewise provided with the breakpoint 84 in bolt 52 and channel 86 in the same manner as stabilizer 82in FIG. 3, but instead of coil springs around the pistons 62 of insert56, stabilizer 90 is provided with a pad 92 comprised of a highlycompressible, springy material that is preferably biologically inertthat functions in the manner of the springs 60 shown in FIGS. 1 and 3.Such materials are known to those skilled in the art but, by way ofexample, certain polyurethanes and other medical grade polymers willfunction for the intended purpose. To insure that pad 92 is retainedbetween the landing 58 of implant 22 and the underside 57 of insert 56,the pistons 62 of insert 56 pass through holes 94 cut through pad 92.

Referring now to FIGS. 6 and 7, a sixth embodiment of a stabilizerconstructed in accordance with the teachings of the present invention isshown at reference numeral 96. Stabilizer 96 is provided with twoinserts 56A and 56B on opposite sides of implant 22, each insert 56A,56B being comprised of a compressible, springy material that ispreferably biologically inert such that the entire insert 56A, 56B isbiased into engagement with the adjacent vertebrae in the same manner ofthe springs 60 (FIGS. 1 and 3), leaf springs 78 (FIGS. 2 and 4), and pad(FIG. 5) when the band 98 that initially encircles the implant 22 (FIG.7) is cut and then removed from the intervertebral space. Many suchmaterials are known in the art, and by way of example, and not by way oflimitation, one such material that is suitable for use in fabricatingthe inserts 56A, 56B is a medical grade polyurethane. As best shown inFIG. 6, the inserts 56A, 56B are shaped with flanges 100 that arereceived within the complementary-shaped undercuts 102 formed on bothsides of implant 22 adjacent the landings 58A, 58B, and the inserts 56A,56B are retained to and in alignment with implant 22 by the interactionbetween the flanges 100, undercuts 102 and the curves surfaces 72A, 72Band 74A, 74B. The three-piece implant 22 of stabilizer 96 is assembledby snapping the inserts 56A, 56B into place on either side of landings58A, 58B, the compressible nature of the material comprising the inserts56A, 56B providing enough resilience that the inserts 56A, 56B must beforced into place and then, once snapped into that place, retainedtherein.

As noted above, the key 46 and keyway 48 on implant 22 and lock 24 maybe reversed from the arrangement shown in FIGS. 1-5 such that key 46 islocated on lock 24 and keyway 48 is located on implant 22, and thestabilizer 96 shown in FIGS. 6 and 7 illustrates such an arrangement.The funnel-shaped portion 47 of the keyway 48 behind the mouth 45 at theend 25 of implant 22, which gradually decreases in width, acts toincrease the ease with which lock 24 is mounted to implant 22 byinsertion of the keys 46 on lock 24 into the respective keyways 48 onimplant 22 and helps to seat lock 24 thereon and align the bore 28 inlock 24 with the bore 30 in implant 22.

Referring now to FIG. 8, there is shown another alternative embodimentof a stabilizer 104 constructed in accordance with the teachings of thepresent invention. Implant 104 differs from the implants 22 ofstabilizer 20 (FIG. 1), stabilizer 76 (FIG. 2), stablizer 82 (FIG. 3),stabilizer 88 (FIG. 4), stabilizer 90 (FIG. 5), or stabilizer 96 (FIGS.6-7) in that the inserts 106 comprising a portion of implant 104 aresized so that the surface 34A of insert 106 extends out of, or are notflush with, the surface 34 of implant 104. As with the inserts 56 ofstabilizer 96 (FIGS. 6-7), the inserts 106 of implant 104 are comprisedof a material that is highly compressible and springy, or spongy, andthat is preferably biologically inert, and is initially compressed by aband in the same manner as shown in FIG. 7. However, rather than beingbiased away from implant 104, the entire insert 106 functions as acushion between vertebrae in the same manner as described in connectionwith the embodiments shown in FIGS. 1-7.

The use of the stabilizer of the present invention in, for instance, amethod of lumbar intervertebral disk stabilization will now bedescribed. Surgery is performed as in a simple diskectomy and theintervertebral disk 20 is exposed through a small laminotomy. Theherniated portion of the disk is removed and any nerve root compressionis corrected. The posterior longitudinal ligament (not shown) and diskcartilage are removed until the surfaces of the bodies of the adjacentvertebrae are exposed above and below the disk space, but the portionsof the disk on either side of the defect are retained.

Using spreaders such as those disclosed in International Application No.PCT/US95/00347, which reference is hereby incorporated into thisspecification in its entirety by this specific reference thereto, theadjacent vertebrae are distracted to open the disk space, and once thedesired “spread” is achieved, an appropriately-sized implant 22 is theninserted into the disk space using the above-described applicator withthe implant 22 oriented so that the top and bottom thereof, i.e., thefirst and second sides 32, engage the bodies of the adjacent vertebrae.As noted above, it is not necessary to remove the remainder of theintervertebral disk or to pack the disk space with cancellous bone chipsas with prior known surgical methods. The positioning of the lock 24 atthe opening to the disk space as described below virtually seals off theopening to the disk space, making the likelihood of recurring herniationof the disk negligible. Further, the posterior longitudinal ligament isleft intact to the opposite side and to the center of the disk space.

The present invention also contemplates the use of a medical gradeadhesive in sealing the opening to the disk space. Another modificationof the method described herein is the use of various hydrogels, eitherwith or without an adhesive, in the intervertebral space. One type ofhydrogel that is suitable for the intended purpose is a group ofpolymers referred to as protein polymers. These polymers are described,for instance, in U.S. Pat. Nos. 5,514,581 and 6,184,348 and in D. C.Martin, et al., “Processing and characterization of protein polymers,”in Protein-Based Materials, K. McGrath and D. Kaplan, Eds. (1996).Various biologically-inert polyvinylpyrolidine (PVP) polymers are alsoknown that function for the intended purpose, as are such polymericmaterials as the modified collagen matrix disclosed in U.S. Pat. Nos.5,147,514, 5,332,475, 5,854,397 and European Patent No. 0411925. Othersuitable materials are known to those skilled in the art and arereferred to collectively herein as hydrogels because of their highlyviscous properties under physiological conditions. These hydrogels areinjected or otherwise introduced into the intervertebral disk spacebefore or after the implant 22 is inserted to fill the space around theimplant and the highly viscous “glob” fills the voids in the disk spaceand functions to help retain the remaining portion of the intervertebraldisk intact and further reduce the likelihood of any recurrentherniation of the disk from the opening into the disk space. Dependingupon the condition of the remaining portion of the disk, if necessary,the disk space may also be injected or otherwise provided with theabove-described medical grade adhesive for the purpose of helping bindthe hydrogel to the disk material and/or helping to maintain theintegrity of the remaining disk material.

Using the applicator, the implant 22 is positioned in the disk space ata position in which the expanded, middle portion and the smaller widthends 25 and 36 of the third and fourth sides 34 of implant 22 contactthe respective lower and upper surfaces of the bodies of the adjacentvertebrae when rotated by approximately 90°. The respective lower andupper surfaces of the vertebral bodies are slightly concave such thatthe larger width middle portion of implant 22 allows the implant 22 toengage substantially more of the surfaces of the vertebral bodies of theadjacent verterbrae than conventional prosthetic devices, therebyproviding increased stability to the implant once further rotation ofimplant 22 in the disk space is prevented as described below.

Once positioned in the disk space so as to provide maximumstabilization, the applicator is detached from implant 22 by backing theapplicator out of the incision in the patient. Lock 24 is then insertedthrough that same incision and, using the key 46 and keyway 48, the bore28 in lock 24 and bore 30 in implant 22 are aligned and the bolt 26 isinserted and tightened to secure lock 24 to the implant 22. Securing thelock 24 to implant 22 in this manner resists relative rotation betweenlock 24 and implant 22 and the bearing surfaces 50 of lock 24 bearagainst the bodies of the adjacent vertebrae to resist rotation of thelock 24 relative to the adjacent vertebrae against which the bearingsurfaces 50 bear. Those skilled in the art who have the benefit of thisdisclosure will recognize that the bearing surfaces 50 bear against thecortical end plate of the respective vertebral bodies, which iscomprised of non-cancellous bone, and provides a hard, relatively smoothsurface against which the bearing surfaces 50 bear. When mounted to theend 25 of implant 22 with the bearing surfaces 50 bearing against one ormore of the adjacent vertebrae, the bearing surfaces 50 of lock 24 areoriented at an angle of approximately 90° to the height of implant 22.The end 40 of lock 24 is preferably supplied in a plurality of differentsizes and shapes other than the square shaped end 40 shown in thefigures so as to allow the surgeon to select an appropriately-sized andshaped lock that provides a close fit with the space between vertebralbodies.

If required at a later date, removal of implant 22 from theintervertebral disk space is accomplished with relative ease compared toconventional implants. The bolt 26 is screwed back out of implant 22 andlock 24 is pulled out of the disk space. An applicator of the typedescribed in the above-incorporated U.S. Pat. No. 5,658,336 is insertedinto the disk space and screwed into the bore 30 in implant 22 and usedto rotate implant 22 by approximately an additional 90°, causing thefirst and second sides, having minimal height, to contact the bodies 12and 14 of adjacent vertebrae 16 and 18 so as to allowposteriorly-directed movement of the implant 22 out of the disk space.

Although described in terms of the embodiments shown in the figures,these embodiments are shown to exemplify the present invention and notto limit the scope of the invention, it being recognized by thoseskilled in the art that certain changes can be made to the specificstructure of the embodiments shown and described without departing fromthe spirit of the present invention. In the case of one such change, thefirst and second sides of the implant are substantially flat but notparallel along their longitudinal axes so that the implant iswedge-shaped. The wedge shape of the implant facilitates insertion ofthe implant into the disk space, the rounded end of the implant reducingthe likelihood of injury to the nerves of the spinal cord duringinsertion into the disk space. Likewise, the width at one end of theimplant can be less than the width at the end, both widths, however,being less than the width in the middle, expanded portion of theimplant. Further, the connection by which lock 24 is mounted to implant22 is capable of being constructed in a manner different than that shownin the figures herein. Another such modification relates to manner inwhich the insert 56 is retained in the first and/or compressed positionproximate landing 58, it being recognized by those skilled in the artthat instead of using the bolt 52 for that purpose, the key 46 andkeyway 48 may be used to restrain movement of insert 56 away fromlanding 58. Another modification relates to the above-described medicalgrade adhesive and protein polymers. As noted above, an adhesive may beutilized to seal the opening to the disk space and/or to facilitatebonding of the protein polymer or other type of hydrogel to theremaining disk material. To facilitate that function, the bore 28 inlock 24 is provided with a reservoir of adhesive that, when punctured byinsertion of the bolt 26 therein, causes the adhesive to exude out ofbore 28 and into the opening to the disk space as the bolt 26 squeezesthe contents from the reservoir as it is tightened against the lock 24.Similarly, implant 22 is provided with a reservoir of protein polymers,for instance, at the end 36 that is punctured by the point of the key 46as the key slides into a keyway such as the keyway 48 on both sides ofthe implant 22 of stabilizer 96 shown in FIGS. 6 and 7. All suchmodifications, and other modifications that do not depart from thespirit of the present invention, are intended to fall within the scopeof the following claims.

1. A method of cushioning between an elongate implant positioned in aspace from which a portion of an intervertebral disk has been removedand the vertebra adjacent the disk space, the implant having asubstantially rectangular cross-sectional shape and a height greaterthan the width of the implant, comprising the steps of: inserting theimplant into the intervertebral disk space with the sides of the implantdefining the height of the implant in contact with the adjacentvertebra, the implant having an insert mounted thereto on a spring andmovable relative to the implant, the insert being restrained againstmovement relative to the implant; rotating the implant along thelongitudinal axis thereof so that the sides of the implant defining thewidth of the implant contact the adjacent vertebra; and releasing theinsert so as to bias the insert away from the implant toward theadjacent vertebra with the spring.
 2. A method of stabilizing twovertebrae comprising the steps of: removing a portion of theintervertebral disk of a patient; inserting an elongate implant havingan insert movably mounted thereto into the space from which a portion ofthe intervertebral disk has been removed; rotating the implant along thelongitudinal axis of the implant after the implant in inserted into thedisk space; restraining the movable insert against movement relative tothe implant until the implant is inserted into the disk space, afterwhich the movable insert is released so as to bias the movable insertinto engagement with a vertebra adjacent the intervertebral disk space;and resisting rotation of the implant along the longitudinal axis of theimplant.
 3. The method of claim 2 additionally comprising filling anyspace between the implant and the two vertebrae with a hydrogel.
 4. Themethod of claim 3 wherein said hydrogel is selected from the groupconsisting of protein polymers, polyvinylpyrollidone polymers, andmodified collagen matrix.
 5. The method of claim 3 additionallycomprising contacting the remaining portion of the intervertebral disk,or the hydrogel, or both the remaining portion of the intervertebraldisk and the hydrogel with a medical grade adhesive.
 6. The method ofclaim 2 additionally comprising sealing the intervertebral disk spacewith a medical grade polymer.
 7. The method of claim 2 wherein theinsert comprises a metal or other relatively incompressible material andis biased away from the implant into engagement with the adjacentvertebra by a spring.
 8. The method of claim 7 additionally comprisingrestraining the insert against movement relative to the implant untilafter the implant is inserted into the intervertebral disk space fromwhich a portion of the intervertebral disk has been removed.
 9. Themethod of claim 2 wherein the implant comprises a metal or otherrelatively incompressible material and the insert comprises a springy,compressible material that provides a cushioning effect when engaged bythe adjacent vertebrae.
 10. The method of claim 9 additionallycomprising compressing the insert before inserting the implant andinsert into the intervertebral disk space from which a portion of theintervertebral disk has been removed and then releasing the insert fromthe initial, compressed state into engagement with the adjacentvertebra.
 11. The method of claim 1 additionally comprising restrainingthe insert against movement relative to the implant until after theimplant is inserted into the intervertebral disk space from which aportion of the intervertebral disk has been removed.
 12. The method ofclaim 1 wherein the implant comprises a metal or other relativelyincompressible material and the insert comprises a compressible materialthat provides a cushioning effect when engaged by the adjacentvertebrae.
 13. The method of claim 12 additionally comprisingcompressing the insert before inserting the implant into theintervertebral disk space from which a portion of the intervertebraldisk has been removed and then releasing the insert from the initial,compressed state into engagement with the adjacent vertebra.
 14. Themethod of claim 1 additionally comprising maintaining alignment of theimplant and the insert while biasing the insert away from the implant.15. The method of claim 1 additionally comprising resisting rotation ofthe implant in the intervertebral disk space.
 16. The method of claim 1additionally comprising limiting the movement of the insert away fromthe implant.
 17. The method of claim 1 additionally comprising resistingmovement of the implant out of the intervertebral disk space.
 18. Themethod of claim 2 additionally comprising resisting movement of theimplant out of the intervertebral disk space.